I'd go get advice from http://www.anandtech.com
Theres more to it than wattage.
I don't even know if your board has a 20 or 24 pin connector. Then theres the P4 plug. Your power supply should have a dual 12v rail, with the Athlon 64. Considering only 1 hdd, and the older vid card, I guess thats not crucial. Anyways, I'd do some research, and I would'nt spend less than $75. Fortron, Sparkle, thats good stuff.